Solid acids are useful for various purposes and, particularly, promising in use as catalyst for various reactions in an industrial process because the process can be simplified, and various types of solid acids have been developed therefore. A typical one of such solid acids is ion-exchange resin which is a polymer having sulfonic acid group. However, the ion-exchange resin has limited uses or using conditions due to defects such as low thermal stability. Nafion or the like that is a high heat-resistance resin has been also developed, but it is too expensive to be used for industrial purposes. In such a situation, carbon-based solid acids which can be obtained by carbonization and sulfonation of an aromatic compound or saccharide have been developed. Such carbon-based solid acids are recently attracting attentions due to inexpensiveness in addition to high performance (high activity), and being tried, as applications thereof, to be used as a proton conductive material or a catalyst for esterification reaction or the like (refer to Non-Patent Document 1, Non-Patent Document 2, Non-Patent Document 3, Patent Document 1, and Patent Document 2).
On the other hand, the solid acids are useful also as catalyst for hydration of olefins. The hydration reaction of olefins is a reaction important for production of alcohols, ketones or the like, and industrially utilized. Isopropyl alcohol, 2-butanol, and methyl ethyl ketone are produced by various methods using hydration of propylene or n-butene (Non-Patent Document 4 and Non-Patent Document 5). At present, a method using sulfuric acid (indirect hydration method) is mainly adapted in plants in the world. However, this method involves many by-products and needs a large quantity of sulfuric acid, causing problems such as sulfuric acid corrosion of an apparatus, reuse treatment of sulfuric acid and liquid waste disposal. Therefore, a direct hydration method or the like using solid acid as catalyst is also being developed, including, for example, a method using, as catalyst, an ion-exchange resin or a solid acid in which a mineral acid such as phosphoric acid is supported by a carrier. However, in these cases, decrease in activity or corrosion of apparatus may be caused by elimination of ion-exchange group (sulfonic acid group) by hydrolysis or desorption of the supported acid from the carrier during reaction, and measures thereto must be taken. Further, the ion-exchange resin-based catalyst has problems such as expensiveness of the catalyst, restriction of reaction temperature from the point of the heat resistance of the resin, and the like.
In the above-mentioned recently-developed carbon-based solid acids, it is considered that various organic substances are usable as the raw material therefor, and examples using condensed aromatics such as naphthalene or coronene, heavy oil or pitch containing the condensed aromatic compound, glucose, starch and the like are disclosed. However, there still exist many unclear points, and it cannot be said that a production method for those having performances of industrially practical level is established. With respect to the hydration reaction of olefins, only an example in which hydration reaction of 2,3-dimethyl-2-butene is carried out at low temperature (70° C.) using such a carbon-based solid acid as catalyst is disclosed without concrete disclosure or suggestion of a catalyst, a reaction condition and the like which are industrially practicable in application to other olefins (Non-Patent Document 6).
In any case, the solid acids mentioned above are recognized to have a problem in the resistance of the acid radical possessed thereby.    Non-Patent Document 1: “Synthesis Condition and Catalysis of Carbon-Based Solid Strong Acid” Atsushi Takagaki, Junko Nomura, Michikazu Hara, Shigenobu Hayashi, and Kazunari Domen, The 85th Spring Meeting of the Chemical Society of Japan (2005), 2B5-43    Non-Patent Document 2: “Synthesis and Characterization of Carbon-Based Solid Strong Acid Having Large Surface Area” Atsushi Takagaki, Junko Nomura, Kazunari Domen, Takashi Tatsumi, Sigenobu Hayashi, and Michikazu Hara, The 96th Meeting of the Catalysis Society of Japan (2005), 4E-21    Non-Patent Document 3: Nature, 438, 10, p. 178, November, 2005    Non-Patent Document 4: Catalyst, Vol. 18, No. 6, p. 180-184, 1976    Non-Patent Document 5: Journal of the Japan Petroleum Institute, Vol. 34, No. 3, p. 201-209, 1991    Non-Patent Document 6: Angew. Chem. Int. Ed., 43, 2955-2958 (2004)    Patent Document 1; Japanese Patent Application Laid-Open No. 2004-238311    Patent Document 2: WO 2005/029508